FR2519066A2 - WELL FILTER OR STRAINER, FORMED BY WINDING FILAMENTS, METHOD AND APPARATUS FOR MANUFACTURING SAME - Google Patents

Abstract

THIS FILTER IS SHAPED BY WINDING WIRES ON A REMOVABLE CHUCK WHICH INCLUDES HELICOIDAL RIBS 18 BETWEEN WHICH ARE DEPOSITED WINDINGS OF WIRES WHICH FORM THE WIRES 38 OF THE FILTER. THE SIDE FACES OF THE RIBS 18 ARE INCLINED IN DIRECTIONS THAT CONVERT OUTWARDS OF A SMALL ANGLEA FROM THEIR BASE, OVER THE LARGEST PART 18A OF THEIR LENGTH, THEN, ON THEIR REMAINING SMALL PART 18B, OF AN ANGLEB BIGGER. THIS PROVISION ALLOWS THE MANUFACTURING ON THE SAME CHUCK OF FILTERS WITH VERY DIFFERENT SLOT WIDTHS WITHOUT SACRIFTING THE BURNING RESISTANCE OF THE FILTERS OR INCREASING IT UNNECESSARILY.

Description

1 - The present invention relates to filters or strainers in material

reinforced plastic

  formed by winding filaments, of the general type -

  described in the main patent application Plus parti-

  culiîrement, the invention relates to a method of

  manufacture of filters or strainers formed by winding-

  filaments on a ribbed mandrel, thanks to which

  filters or strainers that have differed can be produced

  annuities slot widths in order to respond to different conditions of intended use For example, one situation may require a slot width of 1.27 mm while another may require a slot width of 2.54 mm, or even of 3.81 mm In the American patent NO 3,658,128, it is obvious that the

  any slit width required

  would reduce around the diameter of the cylinder filter

  finished drique Such a machining operation would naturally have the effect of cutting a large number of the fibers and destroying the protective resin coating which coats them, thus making the severed ends porous with water or other liquids which, in the absence of an additional protective coating, could infiltrate by capillarity along the fibers and damage them. The large clearance angles of the lateral surfaces of the triangular-shaped wires or bars of the filter of the aforementioned US patent would allow a

  relatively large change in width of -

  However, the triangular shape of the wires shown would result in a significant loss of material from the wires when the diameter of the filter was

  reduced by turning to produce a wide slit.

  The filter would also have a significant decrease in its buckling resistance when it is formed -2- with wide slots since the buckling resistance varies in proportion to the cube of the useful thickness of the wire in the radial direction The draft angles much smaller side surfaces of the filter wires or strainer described in the main patent make it possible to wind the wires forming the filter surface with a much tighter pitch, which makes it possible to obtain "opening surface" percentages of the filter higher than those obtained with the threads of the aforementioned American patent, since the threads are much narrower and much tighter than those described in this patent However, the small clearance angle considerably limits the range of slot widths

  which can be produced on a given mandrel.

  This is due to the fact that the width of the slits is modified by winding more or less large quantities of filaments in the space delimited by the helical grooves of the mandrel, which modifies the height of the wire The small draft angle requires a change relatively large radial height of the wire to produce a relatively small change in the width of the slits Thus, for a given mandrel to be able to produce filters having a predetermined minimum buckling resistance, for a given range of widths of the slits, filters with the narrowest slots would need to have a much larger radial dimension than filters with the widest slots and buckling resistance

much larger than necessary.

  One of the objects of the invention is to provide a filter or strainer formed by winding filaments having a given nominal diameter, which can be manufactured with a wide range of dimensions in width of the slots on a single mandrel. invention is to provide such a filter which requires only a relatively small change in its diameter to produce a significant change in the width of the slits. Yet another object is to provide such a filter as well as an apparatus and a process for its manufacture such that relatively large proportions of the opening surface of the slots and a high buckling resistance can be obtained by using minimum quantities

matter.

  These and other objects are achieved by the apparatus of the invention in which the surfaces of the side walls of the decreasing section ribs or protrusions formed on the mandrel, which form the wires of the surface of the helical filter, have, in their radially innermost parts, a relatively small draft angle and, in their radially outermost parts, a much larger draft angle These different draft angles have the effect that the internal part of the filter wire, which constitutes the greater part of the total wall thickness of the filter, has a relatively narrow cross section and a small draft angle, for example of about 30 The inner part provides the main buckling resistance of the filter The outer part of the filter wire has a much larger draft angle, for example around 150 The large draft angle allows a minimal change in wall thickness for a given change of

dimensions of the slots.

  Other features and benefits of

  the invention will emerge from the description which follows

  given by way of nonlimiting example and with reference to the appended drawing in which FIG. 1 is a side view representing a mandrel of a type suitable for the manufacture of the filter according to the invention; Fig 2 is a side view, partly in section, of a filter to which the invention is applied; Figs 3a and 3b are views, on a larger scale, of some of the ribs, edges or projections of the mandrel of Fig 1, showing their relationship with the filaments which are wound on it to form filters or son between which are respectively formed by wide and narrow filtering slots; Figs 4 a and 4 b are views similar to those of Fig 3 a and 3 b from which they differ only in that they show filter wires between which are formed wide and narrow filter slots and which have been formed on a mandrel of the type described in the main patent; Figs 5 a and 5 b are views similar to those of Figs 3 a and 3 b from which they differ only in that they show filter wires between which are formed wide and narrow filter slots and which have been formed on a mandrel of the type described in the American patent

No. 3,658,128 cited above.

  In Fig 1 to which we will refer, we have generally designated by the reference 10 a

  chuck suitable for use in manufacturing

  cation of the filter or strainer formed by winding filaments according to the invention The mandrel 10 is of the type described in the main patent in that it comprises a removable smooth end part 12, a removable threaded end part 14 and a series of ribbed segments 16 which include ribs 18 The elements of the mandrel are all mounted on a cylindrical support (not shown) which is designed to be removable when the ribbed segments 16 are flattened or disassembled by moving inwards after a filter has been formed on them The ribs 18 formed on each segment are uniformly spaced from each other and the ribs formed on all the segments, when these are assembled, are at the geometrical location of a helix The spaces 20 between the axially adjacent ribs 18 define the shape of the resin-coated filaments (not shown) which are wound therein to form the envelope parts in

  wires of a filter As explained in the main patent

  pal, a single bundle of resin-coated filaments can be wound, longitudinally between the notched end projections 24 and the protruding nipples 26, and circumferentially to produce a filter or strainer having the shape shown in Fig 2 except that the male thread 32 'on the end part

  male 32 is then formed using a lathe tool.

  The female end part 34 of the filter 30 has an internal thread 34 'which is formed directly on the threaded end part 14 of the mandrel. The intermediate part 36 provided with filtering slots is formed by wires 38 wound in a helix which delimit slots 40 The wires 38 are supported in an arrangement spaced from each other by

support bars 42.

  Figs 3a and 3b are sectional views on a larger scale which show some of the ribs 18 of Fig 1 We see that the ribs 18 have their lower wall portions 18a arranged at a small draft angle - ' and their parts of upper or end walls 18 b arranged at a much greater clearance angle f As seen in the

  Fig 3 a, the fact of providing two draft angles.

  allows the wires 38 to be formed in order to obtain a wide slot 6 - of filter width '-> 38, for example of 3.81 mm, and a relatively high cross section with a relatively tight pitch P 18 of 10.160 mm, for example, since the draft angle o is preferably very small, for example 3 Since the draft angle / is much larger, for example 150, we see in Fig 3 b that, when the wires 38 ′ are formed thicker so as to obtain a relatively narrow slot width LV ′ 38, for example 1.27 mm, the additional depth required is much less than if the wall surface 18 b made the same small angle that the surface 18 a We see by considering Figs 4 a and 4 b on which the ribs 118 shown make a constant angle Y of about 150, that it is possible to form the wires 138 to obtain slits W 138 of 3.810 mm or to form the wires 138 'to obtain slits W'138 of 1.27 mm However, the pitch P 118 e our ribs 118 must be increased from 10,160 mm to 12,7 mm

  to allow such a range of slot widths.

  The construction of the prior art shown in Figs Sa and 5b requires that the pitch P 218 between the ribs 218 be increased still further, to 21.59 mm to allow a range of slot widths, Co 38,

  Lut 238 'ranging from 1.27 to 3.810 mm.

  If it is assumed that the ribs of the various mandrels shown in Figs 3 a, 3 b, 4 a, 4 b, Sa, 5 b are dimensioned and spaced so as to produce a filter having an outside diameter of 406.4 mm when the filter slots are 3.81 mm wide, and so as to allow slot openings comprised between 27 and 3.810 mm, and so as to obtain a minimum critical buckling pressure of the resulting filter of 517 k Pa, it can easily be calculated that the improved construction with two draft angles of Fig 3 b has significant advantages For example, -7- the wires 38, 38 'have cross-sectional areas

2 2

  59.55 mm and 95.74 mm respectively compared to

2 2

  69.68 mm and 118.06 mm for wires 138, 138 'and

2 2

  136.77 mm and 178.71 mm for wires 238, 238 'The smallest cross section of the embodiments

  tion of Figs 3 a, 3 b requires fewer winding passes

  LEMENT AND LESS MATERIAL FOR ITS FORMATION The embodiments of FIGS. 3 a, 3 b also have a significantly larger opening surface of the slots LQ 38, '38 per unit length of the filter. Thus, for a given length of the filter , much lower pumping energy will be required to pass a given volume of liquid through the Expressed filter

  in another way, the same amount of surface area

  slot groove can be obtained with a shorter filter length More precisely, in the case of the examples shown respectively in Figs 3 a, 3 b, 4 a, 4 b, 5 a and 5 b We can calculate that the area d opening as a percentage of the total length is respectively 28.5%, 9.6%, 22.8%, 7.7%, 13.4% and 4.5% It can be calculated that the critical buckling pressure of the six examples of filters are 655 k Pa, 1875 k Pa, 531 k Pa, 1517 k Pa, 690 k Pa and 1131 k Pa, respectively, although the embodiment of Fig 5a is slightly better in this respect, the embodiments of Figs 3 a and 3 b have a buckling resistance significantly higher than that of the embodiments of Figs 4 a, 4 b and 5 b We carried out the

  calculations using the dimensions and angles above

  above mentioned and admitting the width and height

  following maximums for each of the embodiments

  tion of Figs 3 a-5 b: 6.35 mm, 12.7 mm; 8.83mm, 17.45mm; 8.83mm, 12.7mm; 11.43mm, 17.45mm; 17.78mm, 15.39mm

and 20.32 mm, 17.6 mm.

  An additional advantage of the invention shown in Figs 3 a, 3 b compared to the modes

  of Figs 5 a, 5 b is that there is a difference

  relatively high height between the height of the wire 38 and that of the wire 38 'compared to that which exists between the wires 238 and 238' Thus, a small variation in the quantity of material wound between the ribs 18 made in order to obtaining a given small slit width W '38 will have much less effect on obtaining the desired slit width than this would be the case for the embodiment of Fig 5b in which very small changes in height 238 'wire can produce very significant changes in

the width W 'of the slots.

  It is preferable that the angle Oi at which the main part 18 has the length of the side of the rib 18

  is formed is not more than about 5 and,

  ference, that it is not greater than about 30 A

  certain obliquity is necessary to facilitate the

  lifting of the mandrel segments by a radial movement inwards with respect to the filter after the filter has been rolled up and hardened However, the use of an angle o too large leads to a waste of material since the capacity of the wires 38, 38 'of buckling resistant filter depends to a much greater extent on the height of the filter than on its width We also consider it preferable that the angle (3 at which the small part 18 b of the length of the side of the rib 18 is formed either of at least 100 and preferably about 150 Since the side wall parts of the wear surface part of the wires 38, 38 ′ are formed by the wall parts 18 b, we see that

  if we used a smaller angle A it would be necessary

  be sure to make the wire 38 'much higher to allow 251906 i -9 to obtain with a single mandrel the variation in width of the slots from d, to' 38 shown in Figs.

38 3

  3 a, 3 b The additional height required would unnecessarily increase the buckling resistance of filters with small slit openings at the cost of a large additional quantity of material. However, the angle "should not be too large either since 'it would then be difficult to obtain a desired uniform slit width c) '38 since it is not possible to fill exactly all the grooves between the adjacent ribs 18 with an identical volume and density of wrapping material constituted by filaments

coated with resin.

-

Claims (9)

CLAIMS -   1 Filter or strainer (30) for wells> of the type described in   main patent, formed entirely of reinforced plastic   ceded by filaments and comprising an elongated part (36) formed   mant filter comprising slots (40), formed by a helical winding, and non-split end portions (32, 34) which are integral therewith, said filaments or strands, each of which is coated with resin, being arranged at the same time in the longitudinal direction and in the circumferential direction over the entire length of the filter,   one of said unsplit end portions (68 ') having a thread   internal female floor (72) formed by at least one layer of filament   circumferential helically wound elements which are positioned   dialing inside all the longitudinal filaments, the se-   second unsplit end part (68 ") having at least one strand of longitudinal filaments (78) positioned radially inside all of its circumferential filaments, characterized in that the cross section of the wires (38, 38 ') which constitute the part of the   filter with slots has, overall, a cross shape   pezoidal whose largest dimension extends in a radial direction with respect to the filter, the upper and lower sides of this cross section being approximately parallel   between them and the sides extending approximately radially conver-   giant inward, the latter two sides being inclined at a relatively small angle (<X) over the greater part (18a) of their length from the bottom side and being inclined at an angle (f) relatively larger on the small part (18 b) of their   length from the upper side.   2 Filter or strainer according to claim 1, characterized in that the angle of convergence of said plus   large part (18a) is not more than about 5.   251906 i -il - 3 Filter or strainer according to claim 1, characterized in that the angle of convergence of said plus   large part (18a) is not more than about 3.   4 Filter or strainer according to claim 3, characterized in that the angle of convergence of said plus   small part (18 b) is at least 100.   Filter or strainer according to claim 3, characterized in that the angle of convergence of said plus   small part (18 b) is about 5.   6 Apparatus for manufacturing a filter or strainer,   as defined according to claims 1 to 5, by winding   of filaments, of the type comprising a mandrel (10) provided with ner-   helical vures (18), formed into several segments and flattened   sand, used to form a bundle of reinforcing filaments   resin coated in a helically wound wire forming the surface of the filter, characterized in that the ribs (18) of the mandrel segments are formed so that their lateral faces, seen in an axial plane of the mandrel, are inclined in directions that converge outward on the largest   part (18 a) of their radial length, starting from their lower part   smaller, with a relatively small angle (Oa) and on the small part   remaining (18 b) of their radial length, of a relative angle (P)   larger, said small part being adapted to be in   contact, on more or less large parts of its extended   dial, with varying thicknesses of resin-coated reinforcing filaments, depending on the desired width of the filter slots between the adjacent wires of the helical winding (38, 38 ') disposed between the adjacent ribs of the mandrel, so that said largest part (18 a) of the radial length of the ribs (18) forms a relatively narrow support base part and of slightly convergent cross section towards 12 - the inside of the filter wires while said small part (18 b) the radial length of the ribs forms a wear surface significantly wider.   7 Apparatus for making a filter or strainer   according to claim 6, characterized in that the angle of convergence   gence of said greater part (18 a) of the radial length   ribs (18) is not greater than about 5.   8 Apparatus for manufacturing a filter or strainer according to claim 6, characterized in that the angle of convergence of said largest part (18a) of the radial length of the   ribs (18) is not more than about 30.   9 Apparatus for manufacturing a filter or strainer according to claim 8, characterized in that the angle of convergence of said small part (18 b) of the radial length of the ribs is at least 100.   10 Apparatus for manufacturing a filter or strainer according to claim 8, characterized in that the angle of convergence of said small part (18 b) of the radial length of the ribs is around 15.